Preparation of tropolones from



United States Patent 015 This invention relates to a process for the production of tropolones from Z-halotropones. More particularly, it relates to such a process wherein the tropolone is prepared by reacting a 2-hal0tropone with formic acid and water.

Previous attempts at preparing tropolones have met with varying degrees of success but none have achieved a simple method suitable ucts accompanied by commercially unacceptable low yields. Typical of the prior methods are the following: bromination of cycloheptane-l,2-dione to give bromotropolonefollowed by catalytic reduction to tropolone, hy-

Serial No. 34,607 filed .iune 8, 1960, and Serial No. 34,609, filed June 8, 1960. These copending applications teach the oxidation of a cycloheptatriene in acid medium to produce a tropylium salt. The tropylium salt is then tion show useful biological properties and tropolone itself may be used as a metal deactivator in motor fuels and rubbers. (See US. Patent No. 2,770,546.)

The present invention provides a process for the production of tropolones which comprises heating a 2-halotropone in a solution comprising formic acid and Water. This conversion is almost quantitative except for the separation of a small quantity of higher molecular weight material.

Any Z-halotropone may be used as a starting material in this process. Thus Z-chlorotropones, Z-bromotropones, 2-iodotropones, and Z-fluorotropones are all suitable starting materials, although 2-chlorotropones are preferred owing to their availability.

The Z-halotropone may be substituted or unsubstituted on the remaining carbon atoms of able substituents on the tropone ring include alkyl radiup to about ten carbon atoms. When one of these substituted 2-halotropones is selected as a starting material, the product of the process of this invention will, of course, be a correspondingly substituted tropolone. The following typical suitable starting materials will illustrate the types of substituted products obtainable:

3,084,193 Patented Apr. 2, 1983 ice 4- (pmethylphenyl)-2-chlorotropone- 4-(p-methylphenyl) tropolone 6- (fl-phenylpropyl) 2-chlorotropone- 6-(fi-phenylpropyl) tropolone Suitable starting materials may therefore be described as compounds having the structural formula wherein each R is individually selected consisting of the alkyl, aryl, alkaryl, aralkyl, and cycloalkyl radicals, and the hydrogen atom. It is preferred that each R is a hydrogen atom or an alkyl group having from 1 to 10 carbon atoms.

Although any halotropones may be used, stituted 2-halotropone as a starting material.

The reaction from the group 10% to about 50% by weight of the formic acid. I formic acid is preferably present in about to by weight of the solution. water both supertemperature.

The tropolone may be recovered appropriate technique.

hexane, octane, carbon tails of the method of carrying out the process of this invention are best illustrated by reference to the following example. It is to be understood that this example is offered for illustrative purposes only and is not to be construed as limiting the invention in any respect.

Example 40.4 grams (0.29 mol) of 2-chlorotropone were dissolved in formed which was filtered. The light yellow filtrate was further acidified to a pH=3, and five times extracted with ether. The ether was dried over Na SO and distiiled off. The residue was distilled in vacuo.

Tropolone:

Boiling point 66-67 C. at 0.1 mm. Hg Colorless crystals Melting point 49-S1 C. Yield: 29.7 g.-=85% of theory.

We claim as our invention:

1. A process for the production of a tropolone which comprises refluxing a Z-halotropone of the formula:

.2. 'A process for'the production of tropolone which .formic acid is present comprises refluxing 2=halotroponein a solution of "formic acid containing 10% to about by weight of water based upon the weight of the formic acid.

3. A process for the production of tropolone which comprises refluxing Z-chlorotropone in a solution of formic acid containing 10% to about 50% by Weight of water basedupon the weight of the formic acid.

4. A process in accordance with claim 3 wherein the in about to by weight of the solution.

5. A process for the production of tropolone which comprises refluxing by boiling at atmospheric pressure a mixture of 2- hlorotropone in a solution of formic acid containing 10% to about 50% by weight of water based upon the weight of the formic acid.

References Cited in the file of this patent UNITED STATES PATENTS Pratt et a1. July 14, 1959 OTHER REFERENCES Chemistry and Industry,

Nozoe 'et ,al.: pages 66-7,

January 15, 1955. 

